Drafting machine



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DRAFTING MACHINE Filed May 9, 1944 8 Sheets-Sheet 2 Q; 26 27 INVENTOR. FoYc/fPoMAWOY,

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DRAFTING MACHINE Filed May 9, 1944 8 Sheets-Sheet 7 262 n INVEN TOR. Pov u. P044520), BY

Patented Dec. 31, 1946 UNITED STATES PATENT OFFICE DRAFTING MACHINE Roy J. Pomeroy, Los Angeles, Calif, assignor, by mesne assignments, of one-sixth to Mildred Hirshstein, one-sixth to Ruth B. Newman, and one-sixth to M. J. Hirshstein, trustee for the benefit of Pearl Hirshstein, all of Cleveland,

Ohio

Application May 9, 1944, Serial No. 534,712

25 Claims.

spective drawing machine adapted to be mounted in cooperative association with a drawing board in such a manner that data ascertained from orthographic projection of an object can be interpreted with the greatest ease and with extreme accuracy to enable the operator'to plot a perspective view of that object with both accuracy and dispatch.

A further object is to provide a perspective drawing machine capable of being used to draw stereoscopic. pairs, which can be viewed with any suitable stereoscopic viewing device for the purpose of studying the device or object revealed in three dimensions.

A further object is the provision of a perspective drawing machine of the general character indicated constructed in accordance with relatively simple design and composed of a small number of parts which are of rugged and rel-. atively inexpensive construction and yet-which can be relied upon to serve accurately and efficiently to carry out the functions for which it has been designed. 1

The invention possesses other objects and valuable features, some of which with those enumerated, will be set forth in the following description of the preferred embodiments ofmy invention illustrated in the drawings accompanying and forming part of the specification. It is to be understood that I do not limit myself to the showing made by the said drawings and description, as I may adopt variations of the preferred embodiments within the scope of my invention as defined in the claims.

Referring to the drawings:

Fig. 1 is a top plan view of a perspective drawing machine incorporating the principles of the present invention.

Fig. 2 is an enlarged detailed view of the straight edge and its actuating carriage, and of the hairline support and its actuating head of the drafting machine illustrated in Fig. 1, portions of the figure being broken away to reduce its sizej Fig. 3 is a transverse, vertical sectional view taken upon the line 33 of Fig. 2 with the direction of view as indicated. v

Fig. 4 is a longitudinal sectional view taken upon the line 4-4 of Fig. 3 with the direction of view as indicated.

Fig. 5 is an underneath plan view of the hairline-actuating head, which may be considered a horizontal sectional view taken on line 5-5 of Fig. 3 with the direction of view as indicated.

Fig. 6 is a top plan view of the straight edge--' actuating carriage, which may be considered a horizontal sectional view taken from the line 66 of Fig. 5 with the direction of view as indicated. 7

Fig. 7 is a detailed view of one of the anchor-; ing blocks whereby the entire drafting machine is mounted, taken in transverse vertical section upon the lines 'l---'! of Figs. 1 and 8 with the direction of view as indicated.

Fig. 8 is a horizontal sectional view taken upon the line 88 of Fig. '7 with the direction of view as indicated. i

Fig. 9 is a vertical sectional view, the lane of section being indicated by lines 9-9 of Fig. 8 and the direction of View by the arrows.

Fig. 10 is a view similar to Fig. 9 but showing the opposite anchoring block; hence, this view may be considered a sectional view taken upon the line Ill-I0 of Fig. 1 with the direction of view as indicated.

Fig. 11 is a schematic View indicating the different steps performed by my improved drafting machine in plotting a perspective view of an object.

Fig. 12 is a view similar to Fig. 11 but indicating the manner in which the drafting machine of the present invention can be employed to draw a stereoscopic pair of perspective views.

Fig. 13 is a view similar to Fig. 1, but showin a modified form of perspective drafting machine of the present invention. 1

Fig. 14 is an enlarged top plan view of the essential mechanism of the drafting machine of Fig. 13, portions of the figure being broken away to reduce its size.

Fig. 15 is a transverse vertical sectional view taken upon the line l5-l5 of Fig. 14 with the direction of view as indicated. Portions of thisfigure also are broken away to reduce its size.

Fig. 16 is a longitudinal vertical sectional view taken upon the line |6|6 of Fig. 14 with the 3 taken on the line |B--|8 of Fig, 16 with the direction of view as indicated.

Fig. 19 is a detail view in longitudinal vertical section taken on the line |9|9 of Fig. 1'? with the direction of view as indicated.

Fig. 20 is a fragmentary plan view of a modified point-finding element.

Referring first to that modification of my invention which is illustrated in Figs. 1 to 10, inclusive, a pair of upper and lower drafting boards 26 and 21 are rigidly mounted on any suitable support such as a drafting table 28, preferably with their adjacent edges in parallel relation and vertically separated far enough to provide a horizontally or transversely extending space 29 therebetween. Each of these drafting boards 26 and 21 provides a drawing area upon which sheets of drawing paper 3| and 32, respectively, can be secured as by thumb tacks 33 and 34, respectively. The space 28 accommodates a pair of anchoring blocks 36 and 31 which "are separated from each other far enough to accommodate a guide bar 38 extending therebetween. As best shown in Figs. 7 and 8, each end of the guide bar 38 is seated within a complementary and closely fitted socket 39 in the'associat'ed head- 36, 3! for the dual purpose of supporting the guide bar 38 rigidly in position extending transversely withrespect to the drawing areas and also 'to maintain the anchoring blocks 36, 31 rigidly at their s'e-'- lected spacing.

Each of the anchoring blocks 36, 31 carries a vertically disposed pin 4|, upon each of which a pair of pulley wheels is journaled. As best shown inFig. 9, the pulley wheels 42 and 43 associated with the anchoring block 36 are rigidly joined together, preferably integrally, whereas the pulley wheels 44 and 46' associated with the anchoring block 31 are separate from each other so that each is enabled to rotate independently of the other. Toward this end the pulley wheels and 46 are each provided with an anti-friction hearing 41, '48, respectively; to mount them upon the associated pin 4|; whereas in the case of the pulley Wheels 42 and 43 which are integrally united, a single bearing '46 will 'sufiic'e to mount them on their associated pin 4|. The pulley wheels of each pair are of different diameter from each other, the upper pulleys 42 and 44 preferably beme of smaller diameter than the lower pulleys 43 and 46. A convenient ratio is 1 to 9, as will appear more fully hereinafter. The smaller pulleys 42 and 44 are preferably, but not necessarily, each of the same diameter and are arranged in planar alignment so that they can carry a belt of flexible metal, stainless steel being suitable for this use because of its relatively high resistance to stretching when subjected to tension. Similarly, the larger pulleys 43 and46 on'o'p'posite sides of the drafting machine, also preferably, but not necessarily, are each of the same diameter and are 'in planar alignmentso that.

they can receive a second flexible ,belt 52, alsoof some relatively unstretchable material; Since the pulleys 42 and 43 are rigidly interconnected, any motion of the belt 52 tending to rotate its pulleys 43 and 46 will be transmitted by the pulley 42 to the other belt 5| but because of the difference in the radii of the pulleys 42 and "43, the belt 5| will move at a lesser rate and consequently through a shorter distance.

v Since the pulleys -44 and46 are'mounted'upon their bearingip'in 4| independently of each other, the necessity for extreme accuracy in sizing the pulleys 44 and 46 is obviated.

tape 52.

A carriage 56 is slidably mounted upon the guide rod 38 and is guided thereby in straightline, reciprocatory movement in a transverse direction with respect to the drawing areas 3| and 32. Preferably this carriage comprises a pair of blocks 57 rigidly interconnected by forward and after bottom webs 58 and 59, respectively, so as to retain the two blocks 51 in a spaced relation. Axially aligned holes 6| are formed in the two blocks 5? through which the guide rod 88 extends. The parts are so p oportioned and arranged that the guide rod 38 fits within the holes 6| with a sliding 'fit so as to assure accuracy of the straight line movement experienced by the carriage 56 upon the rod 38.

The lower run of the tape 52 is fastened to the carriage 56 so that any motion of the carriage 56 on its guide rod 38 will be transmitted to the A convenient method of effecting this attachment is through the expedient of a set screw 62 threaded through the front edge of the web 58 from its extreme forward edge into a passageway 63 which is formed in the web 58 extending from the lateral edge 64 through a central opening 66 and in alignment with a similar passageway '61 at the opposite end of the web 58. One end 68 of the tape 52 is disposed within the passageway 63, whereas the other end 69 of the tape 52 is "rove through the passageway 61, extended across the central opening 66 and also received within the passageway 68 so that by tightening the set screw 62 thereagainst, both ends 68 and 69 of the tape 52 can be anchored together s0 as toma'intain tension in the entire tape 52, and at the same time anchor the carriage 56 to the tape 52 for simultaneous and c0- extensive movement therewith. Since the portion of the end 69 which extends between the two passageways 63 and 61 is unsupported, the tension in the tape 52-can easily be regulated by means ofa second set screw II, also threaded through the web 58 from its extreme forward edge and extending into theicentral opening 66 where it is provided with a pressure shoe I2 pressing against the unsupported portion of the tape 52 between the two passageways 63 and 61. An upstanding flange I6 is formed on the after edge of the web 59, and a bearing plate ll is secured to this flange as by screws -'|8. A bearing 79 carried by the plate provides a pivotal support for an arm 8| which preferably comprises an upper transparent portion 82 and a lower metal portion 83; offset vertically from each other and rigidly interconnected by means of a stub shaft 84' revolubly seated within the bearing 19. Preferably the transparent portion 82 is releasably secured to the stub shaft 84 as by means of a screw 86 connecting the transparent portion 82 to a plate 81 'which'is permanently fastened upon the lower end'of the stub shaft 84. The lower end 83 of the arm 8| is preferably releasably secured to the upperend of the stub shaft 84 as by a set screw 88,'this' construction making for ease ofassembly inasmuch as the stub shaft 84 can beslipped into the bearing 19 from below before the lower portion 83 of the arm 8| is secured thereto. The upper transparent portion 82 may conveniently be composed 'of Celluloid, transparent plastic, or the like, so that when it extends over subject matter appearing upon the drawing'area 3|, it does not operate to obscure the users view of that subject matter. The transparent portion '82 is provided with a hairline 89 extending longitudinally thereof and accurately intersecting the'axis ofthe-stub shaft 84.

Also mounted upon the guide rod 38 for straight-line, reciprocatory motion is head 96 which preferably has the form of a fiat top plate 9 1 to each end of which a bracket 98 is rigidly secured, as by screws 99. Each bracket 98 has a downwardly extending terminal portion IGI and the two portions IIlI of the brackets 98 are provided with axially aligned holes I02 within which the guide rod 38 is slidably fitted. The lower edge portion of the top plate 97 has a depending flange portion 97a which i slidably supported by the upper side of the web 58 of the carriage 56, while the upper edge portion of plate 91 is slidably supported by the flange I6 upstanding from carriage web 59 (see Fig. 4). The brackets 98 are of such length that the space between the downwardly extending portions I UI thereof is materially greater than the overall length of the carriage 56, which is disposed therein, with the result that the carriage 56 and the head 96 are capable of movement along the rod 38 independently of each other. However, since the head 96 is firmly attached, as presently to be described, to-the tape 5I which passes around the smaller pulleys 42 and as, the ratio between the respective rates of movement of the head 95 and the carriage 55 will correspond to that between the respective diameters of the pulley wheels 42 and 43. Since the tape 5| to which the head 96 is attached passes around the small pulley 42 and the, tape 52 to which the carriage is attached passes around the larger pulley 23, any movement of the carriage 55 upon its guide rod 38 will result in simultaneous movement of the head inthe same direction but through a shorter distance. The lower run of tape 5I is attached to head 96 in a manner similar to the attachment of the lower run of the first mentioned tape to carriage 55. A set screw I53 in flange 91a extending from the outer surface of said flange to a tape passageway 33a formed in the flange engages the two ends of the tape and anchors them together and to the head. The tension in the tapeis regulated by second set screw I54 and tape engaging pressure shoe I65 (Fig. 5).

Means are provided for connecting the lower end 83 of the hairline carrying arm 8I to the head 95 so that as the carriage 56 and the head 96 move along the guide rod 38 the arm 89 will be caused to rotate about the axis of'its stub shaft 84, and since the head 96 to which the lower end of the arm SI is connected is moving at a lesser rate than the carriage, the direction of rotation of the arm BI will be that in which the upper end 82 of the arm SI moves in the same direction as the carriage and at a greater rate. In other words, if the carriage 55 and head 95 move to the right as viewed in Fig. 1, say from the full line position to the broken line position on that figure, the transparent portion 82 of the arm 8I will rotate in clockwise direction to assume position of angularity such as that also indicated in broken lines. For the purpose of providing thisinterconnection between the lower portion 83 of the arm 8I and the head 95, an elongated, longitudinally extending slot I56 is provided in the lower portion 83 of the arm, through which a pin I! extends. A head I08 on the lower end of the pin Ill! is slidably engaged within a T- shaped slot I09 in the upper face of the plate 9'! of the head 96, this slot extending in a direction perpendicular to the direction of movement of the head. Although the lower, slotted portion 33 ,ofthe arm 8| closely overlies the upper face of thejplate 91, awasher III] is interposed therebe ell) tween, and preferably the under surface of this washer III] is provided with a noncircular portion III, extending downward into the narrower portion of the T-shaped slot I09 and slidably fitted thereto so that the washer III! is free to reciprocate with respect to the plate 91 without being permitted to turn upon the pin I01. One side of the washer III] is bevelled as indicated at II 2 and preferably is provided with a suitable index mark (not shown) adapted to be read in cooperative association with calibrations H3 and indicia H4 on the upper surface of the plate 91 v to position the pin IIII accurately in the exact portion of the slot I09 decided to meet requirements for any individual drafting problem as will be explained hereinbelow. Also engaged upon the pin I51, Within the slot I 6'. of the arm 8| and resting upon the upper face of the washer HE, is a bushing IIB, the length of which is slightly greater than the'thickness of the portion 83 of the arm so that when the nut II? which is threaded upon the upper end of the pin I01 is tightened, the nut II'I will exert pressure upon the bushing H5, which in turn will press the washer IIli down against the plate .91 while the tension imposedon the pin It? by tightening the nut III will draw the head I98 upwards against the flanges which define the narrower portion of the T slot, thus clamping the pin Ifl'I in fixed position to the plate 91 without, however, restricting the movement of the arm 8 I, which is thus left free to turn upon the bushing I I6 and to partake of that extent of longitudinal sliding movement, which is coincident to the rotary motion of the arm SI about the axis of the stub shaft 84.

A straightedge, preferably in the form of a rule II8 having a beveled working edge H9 is rigidly secured to the carriage 56 as by screws I20 threaded into the web 53. This rule extends downwards over the drawing area 32 from the carriage 56 accurately at with respect to the direction of movement of the carriage and with its working edge I I9 accurately in alignment with the axis of the stub" shaft 84.

Operation A method of hand plotting of a perspective view of an object, starting with a plan view, will now be described and thereafter will be described how the machine of the invention perform-s the same manipulations. Assume that we havethe plan View I2I of Fig. 11, laid out in a desired aspect on the sheet 3I, which has been fastened to the upper portion of a drafting board, sufficient space having been left below to accommodate the sheet of paper 32 or other medium on which the perspective drawing is to be made. A side elevational view I22 is first drawn by lateral projection from elevational view I2I. A point S representing the station point is plotted in fixed position with respect to the views I2I and I22, a horizontal line I23 representing the location of the picture plane is drawn transversely with re-- spect to the drawing board and between the views I2I and I22 and the station point S, and a vertical line I25 is drawn upwards from station point S. The relationship between the line I25 and the projected view I22 determines elevation at which the object to be depicted will be seen in the perspective; the line of intersection of the line I25 with the view I22 determining the eye-level in the final view. Obviously, the view I22 is to be plotted with this in mind. Then to draw a perspective View I 24 of the object as it would appear to a person located at the station point S, and

viewing the object standing erect upon the plan view I2-I with the edges of its base overlyingthe lines of Fig. 11, respectively, representing those edges, the following procedure is carried out.

Each of the significant points of the plan I2I, as A, B, C and D defining the objects top and a, b, c and d defining the objects bottom, are connected to the station point B by a group of lines I26. Then a group I2! of vertical lines I2'IA, I2'Ia, I2IB, I2Ib, etc., are dropped perpendicularly with respect to the picture plane line I23, there being one such line from each point M, N, O and P and m, n. o and p where the lines of sight I26 pierce the picture plane line I23. In a similar manner lines of sight I28 are drawn from the significant points AI, BI, CI, DI, aI, bI, cI and cZI to the station point S, and from the points of intersection of these lines of sight I28 with the picture plane line I23 a group I29 of vertical lines such as A2, a2, B2, b2, etc., are drawn downwards. It will be noted that the point a on the plan view I2I and al on the elevational view I22 represent the point on the base which is nearest the observer. Therefore, a horizontal line I3I is drawn across the sheet 32 upon which the perspective view I24 is being plotted; and the intersection of the line I3I with the vertical line I2I associated with the point a on the plan view I2I, definitely locates the position on the sheet 32 for the point a4 representing in the perspective View I24 the pointin the base of the object nearest the observer. The line I3I is extended horizontally across the sheet 32 to the point I 33 of intersection with the vertical projection line a2 of the group of lines I29 which has been projected vertically downwards from the intersection of the corresponding line of sight I28 with the picture plane line I23. From this point I33 of intersection, a 45 line 'I'34 is drawn to intersect all of the vertical lines I29; and from these points of intersection agroup' I36 of .horizontal lines A3, a3, B3, 113, etc., are projected. Each of these horizontally projected lines of the group I36 intersects the vertically extendingline of the group I2! from the corresponding point in the plan view I2I in a point which definitely locates the positionin the perspective view I24 of the corresponding point of the object. That is to say, where the line A3 of the group of hori- .zontal lines I36 intersects the vertical line [21A subject matter of the present invention makes it possible to plot a perspective view of an object by the same method as that hereinabove -described but considerably more-easily inasmuch as the machine performs certain of the steps of-the described method automatically. The method of using the drafting machine is as follows: As indicated in Fig. 1, the sheet 3'l, upon which the plan and elevational views I2I .and I22, respec tively, are already drawn, is mounted upon the upper drafting board 25: in position for'thetrans parent arm BI to move thereover. The'blank sheet of drawing paper32 ismountedupon-th'e lower drawing board 21' in position for lines to be drawn thereupon along the straightedge II9. As the head 98 moves back and forth along its guide rod 38, the pivot pin 84 whereby the arm BI is connected to the carriage '58 will move in a straight line transversely with respect to the drawing boards. The line of movement thus described by the axis of this pin 84 is indicated at MI and represents the picture plane. However, this line does not have to be drawn since this is one of the steps which use of the machine makes unnecessary. The first step in plotting the perspective view I24 is to draw the base line I42 transversely across the sheet 32 and at selected position between its upper and lower edges. Then the carriage 56 is slid along its guide rod 38 until the hairline 89 meets the point al on the elevational view I22 which represents the point in the base of the object nearest the observer, The arm 8| carrying the hairline 89 is indicated in this position in broken lines in Fig. 1. With the arm GI in this position, a vertical line I43 is drawn upon the paper 32 along the straightedge II9 to intersect the base line I42; and from the point of intersection of the lines I42 and I43, the 45 line I34 is drawn.

Thereafter, the carriage 56 is manipulated so as to cause the hairline 89 to meet each of the other significant points bl, cI and AI, BI and CI in the elevational view I22 and a vertical line I29 is drawn along the straightedge II9 to'intersect the 45 line I34 while the hairline is meeting each of these points. Then a line I36 is projected horizontally across the sheet 32 from each point of intersection between the lines I29 and the 45line I34.

Then the carriage 56 is manipulated to make the hairline .89 intersect each of the significant points A, B, C and D and a, b, c and d, a vertical line I21 being drawn by means of the straightedge H9 for each of the positions of the arm 8| thus obtained. Then, just as .in the manual method, the intersection of corresponding lines I2! and. 136 will locate the corresponding point in the perspective view I24. When all the significant points have thus been plotted, the outline of the object can be completed by interconnecting the plotted points by the appropriate boundary lines I3 thus constructing a complete perspective view I24.

It is clear, therefore, that in order to show that the perspective drawing machine of the present invention operates in the manner described to construct a perspective View I24 which is accurate, it is necessary only to show that while the carriage .55 is being moved, the hairline 89 describes that kind of motion which results in preserving the alignment of the hairline 89 accurately with a given point S which point then will represent accurately the station point.

Because of the described manner of construction of my improved drafting-machine, when the carriage 56 moves along its guide rod 38 the'head 96 will move at a different rate, and the significant feature of the construction is that the ratio of the rateof' movement of the head to the rate of movement of the carriage remains constant throughout their entire range of movement. If the diameters of the upper and lower pulleys are in the ratio of 9 to .10, as has been stated to be preferredthe speed ratio of the two tapes willalsolbe in the ratio of 9 to 10. Since one part of the arm,8l is connected to the head 96 insuch a manner that the extent of horizontal movement of that part of theiarm 8 I' coincides. exactly with the extentofmovement of the" head, whereas another part of the arm is pivoted to the carriage, the differential movement of the head and carriage will cause the arm 8| to swing about the axis of its pivotal connection 84 to the carriage 56, and it is the purpose of this discussion to show that the nature of this movement is such that the arm 8| swings in true rotary motion about a single point with the hairline 89 at all times extending truly radially with respect to that center.

The picture plane line I23 in Fig. 11 can be assumed, for the purpose of this demonstration, to correspond to the path of the pivot pin 84 whereas, another line I5I parallel theretoand slidable therebelow can be assumed to represent the path of that portion of thehead-BE to, which the lower end 83 of the arm-8| is connected. For any position of the head and carriage any line drawn from the picture p ane line I23 to a central point of rotation, say the station point S, will intersect the lower line I'5I. Consequently, when the carriage moves a given distance carrying the pin 84 a given distance, say the distance 13 to m on line I23, the head 95 will move along the line I5I a lesser distance, say the distance 1) to 111.. Similarly, when the carriage moves the distance 1; to 0 along the line I23, the head 96 will move the distance n to 0' along the line I5I. If corresponding points on these two lines are interconnected by lines I52 which lines are then extended until they intersect, it will be found that these lines actually do intersect at a common point, say the point S. This can be proved geometrically as follows:

Since mutually equiangular triangles are simi-. lar. the triangles was and p'm'S are similar.

Since respective sides of similar triangles are proportional Obviously, however, the triangle 2708 Y and D' 'S are also similar, and since respective sides of similar triangles are proportional pS:pS- -oS;o'S

Furthermore, the triangles nos and n'o'S are also similar, and therefore I n0:n'o'=oS;0'S

Since values equal to the same thing are equal to each other, it follows that pm:p'm'=n0:no'

Or, if segments of unequal lengthen two parallel lines" have their respective ends joined by transverse lines which continue until those transverse lines intersect at an external point, those two segments will bear the same ratio to each other as the ratio between any other two segments on the same parallel lines defined by other transverse lines intersecting at the same external point. It is proved, therefore, that since the ratio of the movement of the carriage 56 to that of the head 96 is constant throughout their entire range of movement, the alignment of the hairline 89 with a given point spaced below the paths of movement of the head and carriage will be preserved, and consequently the drafting machine of the present invention can be relied upon to plot accurately the significant points of a perspective view in accordance with the method hereinabove described.

Because the pivot pin I01 is slidable within the T-slot I99, the distance between the pin Ill! and result that the distance of the station point below the path of movement of the head 96 and the carriage 56 can be selected, thus making it possible to predetermine the view point or station point of the perspective. By virtue of the fact that the two tapes travel in a ratio of 10 to 9, the distance between the picture plane pivot 84 and the station point is ten times the distance between the pivots 8t and IE1, thus making for ease in calibration. The calibrations H4 (see Fig. 2) provided upon the upper surface of the head 96 preferably represent the distances of the station point from the picture plane.

Another matter which is subject to a wide range of latitude in accordance with the wishes of the person using the drafting instrument has to do with the angle of vision, i. e. from which side of the object the view being drawn is taken. Before starting to deveop the perspective view I24 from the-plan view I2I, the operator should determine the angularity at which the object is to be viewed before locating the plan view I2I with respect to the station point S, it being remembered that the station point S is fixed so far as distance from etiher of the lateral edges of the drafting board is concerned since it lies at the intersection of all the radial lines along which the hairline 89 can lie. After having decided on just what view of the object is desired, he then should slide the upper sheet of paper horizontally until the plan view assumes the position with respect to the station point S wherein the actual object viewed at that same angle will present the view desired. The equipment then is in readiness for the operator to start drawing the vertical lines I21, it being understood, of course, that the automatic operation of the machine obviates the necessity of drawing the lines of sight I26.

Considering the mechanism of my drafting machine broadly. it will be seen that the arm 8| constitutes a linearly extensive point-finding element for points in the original views laid out on the upper portion of the drafting area, two lorrgitudinally spaced points of this element having been furnished with pivotal connections to the two difierentially traveling belts 5| and 52. The uppermost pivot will be seen to have been connected to the more rapidly traveling belt 52, in this instance to the lower run of said belt; but it will be noted that the pivot connection is at 84, being the upper of the two pivots 84 and I01. And in this embodiment of the invention, the arm, or longitudinally extensive point-finding element, involves a longitudinally extensive hairline 819. Various substitutes for the hairline 89 are possible, however; for instance, in Figs. 13-19'1its place is taken by a fine wire, which of course is the equivalent of a hairline, and my claims referring to a hairline embrace all such linear elements. As a still further modification, however, the hairline may be reduced to a point, e. g. a stylus, which is linearly extensive along the same line that is'occupied by the hairline in the embodiment of Figs. 110. Such a device is shown in Fig. 20, as a variation of the embodiment of Figs, 13-19, and may, of course, be used in connection with the embodiment of Figs. 1-10 if so desired. 1 Y

The rue IIB with its straightedge H9, which may be considered as a linearly extensive point determining element (just as the arm 8I with its hairline 89 is treated as a linearly extensive pointfinding element) is of course subject to modifications similar to. those indicated in the case of the point-finding element.

Fig. 12 indicates another beneficial use to which the drafting machine of the present invention can be placed as the result of the fact that the exact angle of vision can be selected in accordance with requirements of any individual problem, and can also be shifted, so that a second perspective from a different angle of vision can be drawn. Thus two separate perspective views I6I and I62, respectively, in the nature of a stereoscopic pair can be constructed from the plan and elevational viewsI63 and I64,

The preferred method of accomplishing this is as follows:

FOllOWiIlg the drawing of the perspectiv view I6I, which is executed in exactly the same manner as heretofore described, the station point is shifted. This may be done by releasing the tension in one of the flexible belts 5| and 52, so that both the carriage 56 and head 96 may be shifted laterally without relative movement occurring therebetween. Obviously, this may take place, because if either of the belts slip, the driving connection between the two components 56 and 96 is lost. In the present machine, the belt 5I may be de-tensioned to accomplish the purpose stated by loosening the tension adjusting set screw I84. Throughout any such shifting of the carriage 56 and head 96 laterally, without relative movement occurring therebetween, there will obviously be no pivotal movement of the arm 8|. Therefore, with the arm 8| in its perpendicular position, the carriage and headmay be shifted as a unit to any lateral positiomand thearm 8 I will remain in perpendicular position, so that new station points may be obtained, it being recalled that the station point for any adjustment will lie along the edge .I I9 of arm II 8 when the arm BI is in perpendicular position.

Accordingly, to construct the second member of a stereoscopic pair of perspective views, the belt 5 I is loosened, and carriage 56 and head 86 shifted laterally toward the left until hairline 89 of arm 82 coincides with the new line of sight number 2. The distance of shift is based on the interpupillary distance, which is ordinarily about 65 mm. If the scale of the drawing is to be unity, the distance of lateral shift will accordinglybe 65 mm. However, if the scale is to be increased or decreased, the distance of. shift is increased or decreased proportionately to the scale. The lower sheet of paper I32 may at this time be shifted laterally to the right to provide for the correct viewing distance between the two views, as determined by the type of stereoscopic vewing device to be used.

The sheet I32 is illustrated as so shifted in Fig. 12; compare with Fig. '11. The second perspective view I62 may then be drawn, working from plan view I63 in the normal way, and securin elevations by projecting across from perspective view I6I. A pair of perspective views I6I and I62 prepared as thus described may be viewed stereoscopically to show the figure in third dimension. By thisv simple procedure, accurately depicted stereoscopic pairs of highly complicated objects may be drawn, and such complicated objects may thus be readily studied or explained in many cases in which an ordinary simple perspective would not readily reveal sufiicient detail that the objects might otherwise be understood.

.Figs. 13 to 19 illustrate a slightly modified form of the perspective drafting machine of my invention which, however, is adapted for use in the same manner and to accomplish identically the same purposes as my previously described machine. In this modification a, relatively large drawing board -I1I has opposed notches I12 and I13 formed in lateral alignment with eachother in the two lateral edges to receive anchoring blocks I16 and I11, respectively. Within these anchoring blocks, pulley supporting shafts I18 and I19, respectively, are mounted, these shafts lying in the plane of the drafting board HI and parallel tothe lateral edges thereof. One of these shafts, say the shaft I19, is revolubly mounted, for which purpose aligned anti-friction bearings I8I are provided in the side plates I82 of the associated anchoring block I11. 'Rigidlysecured to the shaft I19 are upper and lower driver pulleys I86 and I81 of different diameters, the upper in this instance havin the greaterdiameter, and theratioof the two :again preferably being, 18 to 9.. In the-other anchoring block I 16, the shaft I18 may berigidly mounted as by having its ends fitted in complementary-sockets, since the two pulley wheels I88 and I89 thereon preferably are individually journaled on the shaft I18 as 'by anti-friction bearings. I9I. Preferably, though not necessarily, the idler pulleys I86 and I89 also are of different radius, with their diameters hearing thesame relationship to each other as in the driver pulleys I85 and I 8 1.

.A spacer tube I96 is under compression between the anchoring blocks I16 and I11; and a tie bolt I91 within. the tube L96 so interconnects the two blocks I16 and I11 that when nuts I98 on the ends of the bolt I91 are tightened, the blocks I16 and I11 are pressed firmly-against the ends of the tube.

Also extending between the two anchoring blocks I16 and I11 are two unstretchable flexible belts 28I and 282, preferably steel tapes, interconnecting corresponding pulleys at the two sides of the drafting board, i. e., the tape 28I extends around the two larger upper pulleys I86 and I88, whereas the other tape 282 extends around the two smaller lower pulleys I81 and I89. Due to the difference in the diameters of the two pulleys I86 and I81 which are rigidly interconnected, any movement of the lower tape- 282 on the smaller pulley I81 will result in movement of the upper tape 28I in the same direction but through a greater distance. Moreover, as in the previously described modification, the ratio between the movements or rates of travel of the two tapes 282 and 28I remains constant throughout their entire range of movement.

In this modification the head206 is connected to the lower (slower) tape, 282 which is associated with the smaller pulley.I 81, a clamping screw 281' threaded through a suitable bracket 288 on the carriage 286 being employed for this purpose. In a similar fashion, the carriage 289 is clamped as by a screw 2II to the upper (faster) tape 28I which passes around the larger pulley I 86. Consequently, when the carriage head moves laterally with respect to the drawing board I1 I, the carriage 289 must move in the same direction and through a greater distance as determined by the ratio between the diameters of the pulleys I 81 and I86.

Comparison of Fig. 14 with Figs. 16 and 19 will reveal that in this modification the carriage 289 takes the form of a plate relatively elongated in the direction extending longitudinally of the drafting board, whereas the head 286 comprises a plate of materially greater width than the carriage 289. The head 286 rests upon the upper surface of the carriage 289, preferably being uided for accurate transverse movement with respect thereto by being slidably engaged between the upper and lower shoulders H2 and H3, respectively, in the upper surface of th carriage 299. Since the two tapes 2M and 202 are spaced apart from each other in a direction-extending longitudinally of the drafting board Ill, and since both tapes can be stretched very tightly, a highly rigid structure is developed which permits facile movement of the head 206 and carriage 209 laterally of the drafting board Ill. The structure can be relied upon to guide the two members 206 and 209 in straight line movement with great accuracy, thus avoiding the necessity of providing additional rigid guides. The tape 202 fits within a groove 2i6 in the under surface of the head 200. So nicely does the tape fit within this groove 216 that side play of the head with respect to the tape is prevented, which feature taken in connection with the relatively great width of the head 200 and the correspondingly relatively great length of the tape 202 which is engaged therewith, further enhances the rigidity of the structure.

Rigidly secured upon the head 203, as by means of a suitable mounting block 2, is a guide tube 2!!! extending in a direction perpendicular to the tapes 20| and 202. 218 is split and is provided with an external tapered thread 2l9 upon which a suitable thumb nut 22! is engaged. This nut 22! may be tightened upon its thread 2|9 so as to look a rod 222 having calibrations 220 in selected position with respect to the guide tube 218 through which the rod 222 slidably extends. A knob 223 on the lower end of the rod 222 facilitates longitudinal adjustment of the rod 222 within the tube 2I8 when the nut 22! is loosened. Rigidly secured upon the upper end of the rod 222 is a block 224 which extends a short distance to one side of the rod 222. (See Fig. 17.) The block 224 carries a vertical pivot pin 226, upon the upper end of which a laterally extending bar 221 is pivotally supported. Adjacent the end of the bar 221 remote from the pivot pin 226 a rod 228 is rigidly secured, and this rod 228 eXtends upwards and through a guide tube 229, the support for which is a laterally extending bar 23!. A vertical pivot pin 232 rigid with the carriage 209 pivotally supports the bar 23l, the pivot pin 232 engaging the bar 23! adjacent the end thereof which is remote from its end that carries the guide tube 229.

As in the previously described modification, the carriage 259 also carries an arm provided with a hairline accurately in radial alignment with the axis of the pivotal connection of the arm to the carriage. In this instance, however, the arm and hairline also are of modified form, the former being preferably a rigid tube 234 carried by an offset portion 238 of the pivotally mounted bar 23!, and the latter taking the form of a length of fine piano wire 23% stretched tightly between a head 23! on the outer or upper end of the tube 234 and said offset portion 238. This oifset portion 238 is of such form that its under surface is spaced only slightly above the upper surface of the drawing board I ll 50 that the piano wire 236, which is secured to the offset portion 238 by extending through a vertical hole 239 therein, closely overlies the upper surface of the drawing board IH, as clearly illustrated in Fig. 10. The upper end of the portion of piano wire 226 which passes through the hole 239 is anchored to the bar 23! by means of a nut 2M threadedly engaged upon a stud 242 or the like on the upper surface of the offset portion 233 of the bar 23L A rule 251 is rigidly secured to the lower end of the carriage The lower end of the tube 14 209 as by an angle bracket 252. One edge 253 of the rule 25l which preferably is bevelled is accurately in alignment with the axis of the pivot pin 232 whereby the hairline-carrying arm 234 is pivoted to the carriage.

The manner of operation of this modification of my drafting machine is the same as in the case of the previously described embodiment. Since the carriage 209 upon which the hairline-carrying arm 234 is pivoted is connected to the tape 2! associated with the larger pulleys, and since the head 206 upon which the pivot pin 225 for the rod 228 which slidably engages the hairline-carrying arm 234 is connected to the other tape 202, which moves at a slower rate than the tape 20I, any movement of the carriage 209 will be accom panied by movement of the pivot pin 226 but at a lesser rate. Say, for example, the carriage 209 moves to the right as viewed on Figs. 13 and 14. As stated, this movement will be accompanied by similar movement of the pivot pin 226, but at a lesser rate and, therefore, the rod 228 is forced to assume a position of obliquity as indicated in broken lines in Fig. 13. When thus moving to an oblique position, the rod 228, since it is slidably fitted within the guide tube 229, will impart similar obliquity to the bar 23! and the hairline-carrying arm 234 rigid therewith. Consequently, it may be seen that the action of the hairline-carrying arm in this modification is precisely the same as that of the transparent arm 89 in the previously described embodiment. Therefore, after the apparatus has been shifted so as to make the piano wire 236 register with a given significant point on one of the plan views, the rule 25I can be relied upon to serve as a straight-edge along the edge 253 of which a vertical line can be drawn to indicate the proper position between the 1ongitudinal edges of the drawing board for the corresponding point in the perspective view being constructed.

Considering the mechanism of Figs. 13-19 in a broad sense, it will be evident that, as in the mechanism of Figs. l-10, there is a linearly extensive point finding element having two pivot connections to the two belts. In effect, the tube 234 carrying the hairline, or fine wire 236, and the rod 228, constitute an arm having the two effective pivot connections 232 and 226 to the belts 29! and 202, respectively, and this arm I refer to broadly as a linearly extensive point-finding element. The effective arm length furnished by the rod 228, and hence the relative speeds of travel of the carriage and head, is of course variable through longitudinal adjustment of the rod 222, as aforesaid. As previously brought out, this adjustment determines the distance between the picture plane (transvers plane through pivot 232) and the station point about which the hairline 236 will rotate.

Fig. 20 shows a modified form of linearly extensive point-finding element, in which the linear hairline is substituted for by a point or stylus which is extensive along the line of the hairline.

The bar 23! pivoted at 232 to the carriage 229 in this instance carries a guide tube 260 which telescopically receives a linearly extensive tubular arm 26| carrying at its end a stylus 262 whose point 263 is closely spaced to the drawing sheet, and traces along the line of the hairline of the earlier described embodiments when the arm '26! is extended or retracted. Thus, with this embodiment, instead of aligning a hairline with significant points of the views depicted in plan and elevation on the upper portion of the drawlng area, the arm 26I is pulled out to the proper extension that the stylus will coincide with each such point in turn. And'of course a similar modification is possible in the case of the straightedge 25!. This stylus type of linearly extensive point finding or determining element has particular application in certain modified forms of my invention to be disclosed in subsequent applications, but is disclosed here to indicate partially the range of equivalent forms that are contemplated as falling within the expressions linearly extensive point-finding or point-determining elements.

I have now disclosed certain present illustrative embodiments of my invention in considerable de tail. It will, of course, be understood that this is for illustrative purposes only, since various changes in design, structure and arrangement may be made without departing from the spirit and scope of the invention or of the appended claims.

I claim:

1. Apparatus for making perspective drawings comprising a base defining a drawin': area, a linearly extensive point-finding element overlying an upper portion of said drawing area, difierentially operable means connected to longitudinally spaced points of said linearly extensive element adapted to move said points transversely across a medial portion of said drawing area in parallel paths in the same direction at a predetermined speed ratio whereby said point-finding element is swept angularly over said upper portion of said drawing area, and a linearly extensive perspective view pint-determining element carried with one of said spaced points and lying in a line extending over the lower portion of the drawing area in a direction perpendicular to said parallel paths.

2. Apparatus for making perspective drawings comprising a base defining a drawing area, a linearly extensive point-finding element overlying an upper portion of said drawing area, differentially operable means connected to longitudinally spaced portions of said linearly extensive element adapted to move said portions transversely across a medial portion of said drawing area in parallel paths in the same direction at a predetermined speed ratio, other than unity and in such arrangement that the uppermost of said portions travels at a faster rate than the lowermost of said portions, whereby said point-finding element is swept angularly over said upper portion of said drawing area, and a linearly extensive perspective View point-determining element carried with the uppermost of said spaced portions and lying in a line extending over the lower portion of the drawing area in a direction perpendicular to said parallel paths.

3. Apparatus for making perspective drawings comprising a base defining a drawing area, a linearly extensive point-finding element overlying an upper portion of said drawing area, means for carrying and swinging said element about a predetermined center embodying a pair of fiexible endless belts having runs extending parallel to one another across a medial portion of said drawing area, means pivotally connecting longitudinally spaced portions of said linearly extensive element one to one of said runs and the other to the other of said runs, and means interconnecting said belt runs for movement in the same direction at a predetermined speed ratio embodying a pair of interconnected pulleys of differential diameters, one engaging one of the belts and the other engaging the other of the belts, and a linearly extensive point-dcsermining element carried with one of said spaced portions and lying in a line extending over the lower portion of said drawing area in a direction perpendicular to the paths of movement of said belt runs,

4. Apparatus for making perspective drawings comprising a base defining a drawing area, a linearly extensive point-finding element overlying an upper portion of said drawing area, a pair of flexible belts having horizontal runs extending parallel to one another transversely across said drawing area, means mounting and constraining said belts to travel at a predetermined speed ratio other than unity, means pivotally connecting two longitudinally spaced portions or said linearly extensive element to said belt runs, the uppermost of said portions to the faster travelling belt run, and the lowermost of said portions to the slower travelling belt run, and a linearly extensive point-determining element carried with the uppermost of said spaced portions and lying in a, line extending over the lower portion of said drawing area in a direction perpendicular to the paths of movement of said belt runs.

5. Apparatus for making perspective drawings comprising a base defining a drawing area, a linearly extensive point-finding element overlying an upper portion of said drawing area, a pair of endless belts having parallel horizontal runs extending transversely across a medial portion of the drawing area, one above the other, means mounting and constraining said belts for travel at a predetermined speed ratio other than unity, means pivotally connecting two longitudinally spaced portions of said linearly extensive element to said belt runs, the uppermost of said portions to the faster travelling belt run, and the lowermost of said portions to the slower travelling belt run, and a linearly extensive point-determining element carried with the uppermost of said spaced portions and lying in a line extending over the lower portion of said drawing area in a direction perpendicular to the paths of movement of said belt runs.

6. Apparatus for making perspective drawings embodying a base defining a drawing area, arm means overlying a portion of said drawing area and adapted to be angularly swung about a predetermined center point, means for so swinging said arm means comprising mean pivotally engaging two longitudinally spaced points of said arm means and operable to move said points transversely across said drawing area at rates of travel bearing a predetermined constant ratio to one another, and a second arm means carried with one of said points and extending in a direc tion always at right angles to the direction of travel of said point.

'7. Drawing apparatus of the character described co-mprising a base defining a drawing area, pairs of axially aligned pulleys journalecl on axes perpendicular to the drawing area adjacent the two lateral edges of said drawing area, and intermediate upper and lower portions of said area, the pulleys of at least one of said pairs being interconnected for simultaneous rotation and having differing radii, a pair of flexible endless belts each engaged upon one pulley of each of said pairs, in such manner as to provide belt runs extending over said base transversely of the drawing area between corresponding pulleys of the two said pairs, an arm means movable over the upper portion of the drawing.

area, and means pivotally connecting two longitudinally spaced portions of said arm means to two of said belt runs that travel in the same direction, the upper of said portions, to the one of said runs associated with the pulley of larger radius, and the lower of said portions, to the belt run associated with the pulley of lesser radius.

8. Drawing apparatus of the character described comprising a drawing board, pairs of pulleys journaled adjacent the two lateral edges of said board on axes parallel to the surface of said board and parallel to the lateral edges thereof, the pulleys of at least one of said pairs being interconnected for simultaneous rotation and having differing radii, a pair of flexible belts, each engaged upon one pulley of each of said pairs, and having one run extending transversely across above the drawing board'and one run extending transversely across beneath the drawing board, an arm means, and means pivotally connecting longitudinally spaced portions of said arm means to the two belt runs that are above the drawing board, the upper of said portions to the one of said runs associated with the pulley of larger radius, and the lower of said portions to the belt run associated with the pulley of lesser radius.

9. Apparatus for making perspective drawings comprising means defining a drawing area, a carriage movable with respect thereto in a predetermined path, means carrying a hairline pivotally mounted on said carriage and extending therefrom over a portion of said drawing area to one side of said predetermined path, a straightedge rigid with said carriage and extending over another portion of said drawing area in a direction perpendicular to said predetermined path, and means operable as said carriage moves along said path for moving said hairlinecarrying means in a rotary motion about the axis of its pivotal mounting at a rate bearing a predetermined relationship to the rate of movement of said carriage.

10. Apparatus for making perspective drawings comprising means defining a drawing area, a carriage movable with respect thereto in a predetermined path, means carrying a hairline pivotaliy mounted on said carriage and extending therefrom over a portion of said drawing area to one side of said predetermined path, a straightedge rigid with said carriage and extending over another portion of said drawing area in a direction perpendicular to said predetermined path, means operable as said carriage moves along said path for moving said hairline-carryin means in rotary motion about the axis of its pivotal mounting at a rate bearing a predetermined relationship to the rate of movement of said carriage, and adjustment means for varying the ratio of said rates to each other.

11. Apparatus for making perspective drawing comprising a carriage, means mountin said carriage for straight line, reciprocatory movement, a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, means pivotally connecting said hairline-carrying means to said carriage, means pivotally connecting said hairline-carrying means to said head at a pivot point spaced from the pivotal connection of the hairline-carrying means with the carriage, and means interconnecting said head and carriage for moving said head with respect to said carriage through a distance bearing a predetermined constant relationship to the distance through which said carriage moves.

12. Apparatus for making perspective drawings comprising a carriage, means mounting said carriage for straight line, reciprocatory movement, a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, means pivotally connectin said hairlinecarrying means to said carriage, means pivotally connecting said hairline-carrying means to said head at a pivot point spaced from the pivotal connection of the hairline carrying means with the carriage, means interconnecting said head and carriage for moving said head with respect to said carriage through a distance bearing a constant relationship to the distance through which said carriage moves, and a straightedge rigid with said carriage extending perpendicular to the path of movement thereof.

13. Apparatus for making perspective drawings comprising a carriage, means mounting said carriage for straight line, reciprocatory movement, a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, a pair of pivots spaced apart in the direction of said hairline and pivotally connecting said carrying means respectively to said carriage and to said head, one of said pivots being adjustably arranged for variance of the distance between said pair of pivots, means interconnecting said head and carriage for moving said head when said carriage moves, in such manner that the ratio of movements of said head and said carriage remain constant throughout their entire range of movement, and a straightedge mounted rigidly upon said carriage with its working edge perpendicular to the path of movement thereof.

14. Apparatus for making perspective drawings comprising a carriage, means mounting said carriage for straight line, reciprocatory movement, a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, a pin pivotally connecting said carrying means to said carriage, a second pin slidably engaged within a slot extending transversely of said head and within a slot in said carrying means, means for fastening said second pin in selected position within one of said slots, and diiferential driving means actuated by said carriage during movement thereof for moving said head at a rate bearing a constant relationship to that of said carriage.

15. Apparatus for making perspective drawings comprising a. carriage, means mounting said carriage for straight line, reciprocatory movement,

a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement,

a pin pivotally connecting said carrying means to said carriage, a second pin extending through a slot in said carrying means, a head on said second pin slidably seated within a T-slot extending transversely of said head, a nut threaded on said pin, a bushing on said pin and slidably disposed within said slot in said carrying means, said bushing being longer than the thickness of the associated portion of said carrying means whereby tightening of said nut operates to fasten said head in selected position within said T-slot without tightening said carrying means with respect thereto, and differential driving means actuated by said carriage during movement thereof for moving said head at a rate bearing a constant relationship to that of said carriage.

16. Apparatus for making perspective drawings comprising a carriage, means mounting sa1d carriage for straight line, reciprocatory movement, a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, a pair of pivots spaced apart in the direction of said hairline and pivotally connecting said carrying means respectively to said carriage and to said head, and differential driving means actuated by said carriage during movement thereof for moving said head at a rate bearing a constant relationship to that of said car riage.

17. Apparatus for making perspective drawings comprising a carriage, means mounting said carriage for straight line, reciprocatory movement, a head cooperatively associated'with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, a pair of pivots spaced apart in the direction of said hairline and pivotally connecting said carrying means respectively to said carriage and to said head, a pair of axially aligned pulleys adjacent each end of said carriage-mounting means and journaled for rotation about an axis fixed with respect thereto, the pulleys of at least one of said pairs being of diiierent radius from each other and being interconnected for rotation together, flexible belts engaged upon and interconnecting corresponding pulleys of both of said pairs, and means associated with each of said belts for connecting them respectively to said carriage and to said head.

w n apparatus of the character described comprising a drawing board, a pair of transversely separated anchoring blocks rigid therewith, a guide rod rigid with and intercon meeting said anchoring blocks, a pair of axially aligned pulleys journaled on each of said anchoring blocks, said pulleys of at least one oi'said pairs being of different radius and being interconnected for simultaneous and coextensive rotation, flexible belts engaged upon and interconnecting the larger and smaller pulleys, respectively, of both of said pairs, a carriage slidably engaged on said guide rod, a head slidably engaged upon said guide rod independently of said carriage for movement parallel to the belt runs between said pulleys, means clamping one of the runs of aid belt on said larger pulleys to said carriage for coextensive movement therewith, means clamping said head to the corresponding "run of the other of said belts, an arm pivoted intermediate its ends to said carriage and extending therefrom over the upper portion of said drawing board, the lower end of said arm overlying a portion of said carriage and having a longitudinal slot therein, a pin rigid with said head and extending through said slot whereby said lower end of said arm is moved in the same direction as said carriage when said carriage is moved but at a slower rate, and a straightedge rigid with said carriage and extending therefrom over the lower portion of said drawing board with its working edge perpendicular to said guide rod.

19. Apparatus for making perspective drawings comprising a carriage, means mounting said carriage for straight line, reciprocatory movement, a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, means pivotally connecting said carrying means to said carriage, a rod parallel to said hairline and connected to said carriage for axial movement with respect thereto, means pivotally connecting said rod to said head, and difierential driving means actuated by said carriage during movement thereof for moving said head at a rate bearing a constant relationship to that of said carriage.

20. Apparatus for making perspective drawings comprising a carriage, means mounting said carriage for straight line, reciprocatory movement, a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, means pivotally connecting said carrying means to said carriage, a rod parallel to said hairline and connected to said carriage for axial movement with respect thereto, means pivotally connecting said rod to said head, at least one of said pivotally connecting means being adjustably arranged for variance of the distance between them, releasable means for locking said adjustable connecting means in selected position, and differential driving means actuated by said carriage during movement thereof for moving said head at a rate bearing a constant relationship to that of said carriage.

21. Apparatus for making perspective drawings comprising a carriage, means mounting said carriage for straight line, reciprocatory movement, a head cooperatively associated with said carriage and mounted for reciprocatory movement with respect thereto and parallel to that of said carriage, means carrying a hairline extending from said carriage in an angular direction with respect to the path of said straight line movement, means pivotally connecting said carrying means to said'carriage for rotary movement about an axis with respect to which said hairline is radially disposed, a rod parallel to said hairline and connected to said carriage for axial movement with respect thereto, means pivotally connecting said rod to said head, said rod being laterally offset to the same side of and the same distance from both of said pivotally connecting means, at least one of said pivotally connecting means bein adjustably arranged for variance of the distance between them, releasable means for locking said adjustable connectingmeans in selected position,

and differential driving means actuated by said carriage during movement thereof for moving said head at a rate bearing a constant relationship to that of said carriage.

22. Apparatus for making perspective drawings comprising a base defining a drawing area, a linearly extensive point-finding element overlying an upper portion of said drawing area, means for carrying and swinging said element about a predetermined center point including a pair of means operatively engaging and adapted to move two longitudinally spaced portions of said element in parallel horizontal paths transversely across said drawing area at a predetermined speed ratio, with the uppermost of said points travelling at the greater speed, the length of said element included between points of engagement with said pair of means being extensible and contractible as said element swings from and toward a vertical position, and a vertically arranged linearly extensive perspective view point-determining element carried in transverse horizontal travel across said drawing area with the uppermost of said spaced portions of said point-finding element.

23. Apparatus for making perspective drawings comprising a base defining a drawing area, a linearly extensive point-finding element overlying an upper portion of said drawing area, a pair of flexible belts having horizontal runs extending arallel to one another transversely across said drawing area, means mounting and constraining said belts to travel at a predetermined speed ratio other than unity, two spaced pivot means pivotally connecting two longitudinally spaced portions of the lower section of said element to said belt runs, the uppermost of said portions to the faster travelling belt run, and the lowermost of said portions to the slower travelling belt run, said element being arranged for extension and contraction of that portion of its length included between said pivot means with movement of said element from and toward a vertical position, and a vertically arranged linearly extensive perspective view point-determining element carried in 22 transverse horizontal travel across said drawin area with the uppermost of said spaced portions of said point-finding element.

24. Apparatus for making perspective drawings comprising a base defining a drawing area, a linearly extensive point-flnding element overlying an upper portion of said drawing area, a pair of flexible belts having horizontal runs extending parallel to one another transversely across said drawing area, means mounting and constraining said belts to travel at a predetermined speed ratio other than unity, means furnishing a pivot connection for a point on said element to one of said belt runs, means furnishing a longitudinal slide-pivotal connection for a portion of said element longitudinally spaced from the first-mentioned belt connected point, to the other of said belt runs, the uppermost of said connections being made to the faster travelling belt run, and a vertically arranged linearly extensive perspective view point-determining element carried in transverse horizontal travel with the faster travelling belt run.

25. Apparatus formaking perspective drawings comprising a base defining a drawing area, a linearly extensive point-finding element overlying an upper portion of said drawing area, a pair of flexible belts having horizontal runs extending parallel to one another transversely across said drawing area, means mounting and constraining said belts to travel at a predetermined speed ratio other than unity, two spaced pivots pivotally connecting two longitudinally spaced points of the lower section of said element to said belt runs, the uppermost of said points to the faster travelling belt run, and the lowermost of said points to the slower travelling belt run, telescoping means in said element between said pivotally connected points, and a vertically arranged linearly extensive perspective view pointdetermining element carried in transverse horizontal travel with the faster travelling belt run.

ROY J. POMEROY. 

